Pack your bags. Geology is the goal, but anything natural or prehistoric along the way is fair game as we head out.

Tag Archives: cascade

At the east end of Lake Superior, Highway 17, the Trans-Canada Highway, crosses the Harmony River on the east side of Batchawana Bay near Harmony Beach. (This is the second bay on Lake Superior north of Sault Ste. Marie.) Just upstream from the bridge, a wayside park provides access to Chippewa Falls, which is actually two cascades 150 feet apart. The original bedrock is 2.7 billion-year-old pink granite, but, at the lower falls, it is still covered with a remnant of a 1.1 billion-year-old lava flow called the Keweenawan basalt that was extruded during the Grenville orogeny. The contact between the two rocks types represents 1.6 billion years of erosion that brought the granite to the surface by the time of the volcanic activity. A lateral fault cuts through both layers on the north side of the present-day lower falls (out of sight in the two opening photos).

A remnant of the gray, 1.1 billion-year-old lava flow called the Keweenawan basalt, extruded during the Grenville Orogeny (mountain-building episode), covers the 2.7 billion-year-old pink granite next to the lower Chippewa Falls (hidden right rear).

Potholes in the Keweenawan basalt are geologically-recent erosion features resulting from swirling eddies carrying abrasive sand, gravel and cobbles in a circular motion that grinds them down into the base rock.

A small remnant of the gray Keweenawan basalt covers the pink granite as we climb toward the lower Chippewa Falls.

erosion along several of the many joints in the pink granite provides a partial view of the lower Chippewa Falls

the lower Chippewa Falls

several visitors provide scale next to the crest of the lower Chippewa Falls

view further upstream looking across the pink granite bedrock toward the upper Chippawa Falls at upper right

The upper falls was created by a vertical diabase dike cutting across the granite. Here the fault displaces the dike by 30 feet upstream on the northwest side of the river. The upper falls can be reached by an 800 foot trail from the parking area although we didn’t have time to try it. Apparently the trail continues another 500 feet upstream to a bed of large boulders. If you were able to travel six miles further upstream, you’d reach the confluence with the Chippewa River.

The upper Chippewa Falls was created by a vertical, gray, diabase dike cutting across the pink granite. Here the fault displaces the 65-foot thick dike by 30 feet upstream on the northwest (left) side of the river.

“A plaque erected by the Ontario Motor League highlights Batchawana Bay (at Chippewa Falls) as the mid-point in the longest national highway in the world — the Trans-Canada Highway.” (from the Batchawana Bay PP page )